Materials link you to the larger world; to factories, smokestacks, mines, and oil-rigs, or to fields, forests, sun and soil. The materials used in a building can bring with them a large carbon debt that will take decades of operational efficiency to pay off, or they can turn a house into a carbon sink that’s already carbon-negative on day one.
This was the message delivered at the Better Buildings by Design conference, February 2020, by Chris Magwood of the Endeavour Centre in Peterborough, Ontario, and Jacob Racusik and Ace McArleton of New Frameworks in Burlington, VT, in a talk titled “Carbon Drawdown Now.”
The planet exchanges carbon among five spheres; the biosphere, pedosphere (soil layer), lithosphere earth’s crust and mantle, atmosphere, and hydrosphere (waters). Carbon sinks absorb more carbon than they release. According to the speakers’ analysis, buildings built with biogenic materials can become the world’s sixth carbon sink, with a surprisingly large impact. Project Drawdown identifies twelve building-based climate interventions. Using a biogenic supply chain can nearly double that impact.
Biogenic materials are mostly plant-based (sheep-wool insulation is second-generation plant-based, since sheep eat plants). Often, they can be swapped out one-for-one with synthetic materials. Simply choosing blown-in cellulose insulation over synthetic spray foam sequesters plant-based carbon for the lifetime of the building. Biogenic materials include wood, wood fiber board, hempcrete, straw board, straw bales, bamboo, cork, rice straw MDF (medium-density fiberboard) mycelium, cellulose, and ReWall (sheathing board made from recycled, compressed drinking cartons). Many of these choices don’t require a radical rethink but make a large impact on a building’s carbon debt.
Plant-based building materials sequester carbon in two ways. First, plants use it to build their own structures which are then preserved for the lifetime of the building. Second, plant roots build a certain amount of carbon into the soil, depending on how they are grown. Wood, for instance, should be sustainably harvested from well-managed local forests for maximum carbon-sequestration. Crop-based materials should be regeneratively farmed using minimal tillage.
Paying attention to how materials are grown closes the loop between construction and the farms and forests where the supply chain originates. It creates community and brings profitable activity to rural areas. One example is a new factory next to a California rice farm that converts leftover straw into rice straw board, a form of MDF. Formerly, the rice stalks were rotted by flooding after harvest, releasing copious amounts of methane. Now, the carbon drawn out of the air during the growing season is sequestered in buildings, where it will likely remain for at least 100 years. Sequestration happens now, at the beginning of the building’s lifetime, which is when we urgently need to draw down carbon to avoid the worst effects of climate change. Under this model, operational savings over the building’s lifetime are an added benefit.
Magwood of the Endeavour Centre offers four models for constructing a house, with escalating degrees of care for the environmental impact of materials. His conventionally built home has a net-emission debt of 207 tons of carbon. Without deviating far from current building norms, the same house can become a net carbon sink (-15 tons). By making the absolute best choices, using materials that currently exist but may be uncommon, a builder can achieve -117 tons of carbon sequestered.
He has found that choosing materials based on their global-warming potential reduces other kinds of negative impact, such as ozone depletion, acidification, and depletion of fossil fuels. These materials contain no noxious chemicals, so are healthier to live with, recyclable, or biodegradable.
Materials choice in retrofits and weatherization can also sequester carbon. Efficiency Vermont is currently conducting a study to ensure that weatherization materials do not cause unintended environmental damage. Affordability is also a consideration Generally, it seems that materials with high embodied carbon do not increase the cost of projects.
For all construction to become carbon-negative by 2030, builders should stop using high-carbon materials now, move to readily available, moderate-carbon materials within two to three years, go to carbon-zero buildings in three to five years, and aim for all buildings being net-negative in five to ten years. Can we? Watch the video and judge for yourself. It can be viewed at https://www.efficiencyvermont.com/trade-partners/bbd/keynote. You may come away feeling quite inspired.
Jessie Haas has written 40 books, mainly for children, and has lived in an off-grid cabin in Vermont.